The aziridine is a cYclic compound having a 3-membered ring with a large distortion. It has both ring-opening reactivity and the reactivity of an amine, and is useful as an intermediate for various compounds. In particular, ethylenimine has already gained widespread acceptance in the industry as a material for agricultural chemicals and pharmaceuticals and for amine-type polymers which are useful as textile treating agents.
A generally well-known method of producing an aziridine compound is typically a method of producing ethylenimine which comprises treating monoethanolamine sulfate in the liquid phase with a concentrated alkali solution, which has already been industrially practiced. This method, however, has many defects in industrial practice. For example, because of the need for using large amounts of sulfuric acid and an alkali as subsidiary materials, it has low productivity. Moreover, inorganic salts of low utilitarian value are formed as by-products.
In an attempt to remove the defects of aziridine production by such a liquid-phase method, various methods have been reported recently for the direct production of an aziridine compound by intramolecular dehydration reaction of an alkanolamine in the vapor phase in the presence of a catalyst without using subsidiary materials (U.S. Patents Nos. 4301036, 289656, 4337175 and 4477591, and European Laid-Open Patent Publications Nos. 227461, 228898 and 230776). These prior attempts, however, were directed mainly to catalysts for the intramolecular dehydration reaction in the vapor phase, and failed to propose an industrial process for obtaining the desired aziridine compound from the gaseous reaction product mixture.
In the production of an aziridine compound from an alkanolamine by the vapor-phase method, the reaction product gas contains by-products such as a carbonyl compound of the following general formula (III) ##STR4##
wherein R is as defined in formula (I) above, which corresponds to the starting alkanolamine, and various amines. If the starting alkanolamine is monoethanolamine, monoisopropanolamine or 2-amino-l-butanol, the corresponding carbonyl compound of formula (III) is acetaldehyde, acetone or methyl ethyl ketone, respectively. For example, U.S. Pats. Nos. 4,337,175 and 4,477,591 describe that in the production of ethylenimine from monoethanolamine, acetaldehyde is formed as a main by-product and monoethylamine and pyrazines are also formed as by-products. European Laid-Open Patent Publications No. 227,461, 228,898 and 230,776 also describe that the main by-products are the carbonyl compounds of formula (III) and various amines.
In the industrial production of organic compounds by a vapor-phase method, it is the general practice to recover the desired product from the vaporphase reaction product and purify it in order to obtain the final product. The industrial production of aziridine compounds from alkanolamines by the vapor-phase method, however, has the following problems. First of all, the aziridine compounds of formula (II) generally have a low boiling point and a very high vapor pressure. Moreover, they are very reactive, and liable to undergo polymerization and other reactions. Furthermore, among the various by-products formed in the vapor-phase method as mentioned above, the carbonyl compounds tend to react with the desired aziridine compounds and form adducts. Hence, the yield of the desired aziridine compounds is reduced. These problems should therefore be taken into consideration in producing aziridine compounds by the vapor-phase method.